Well, the reason is because I'm in a very peaceful relationship w/ my only competition (India). I'm about 110 pts. up on the histograph scale, but India is killing me in tech. I'm in Republic but have a large military cost which is keeping my tech rate at 20%. With two early conquests, I got a large territory quickly and have spent the past 150 years building infrastruture.
I feel the space ship race is the only way I could lose at this point. The year is roughly 1815. One civ, Aztecs, I must finish off because they would vote against at the UN. The fourth civ, Greece, is doomed to be exterminated because I feel they would also vote for India.
This is my second attempt on Regent and best chance of winning my first Regent game, ever. I'm unsure of attacking India w/ its tech lead. We both have cavalry and riflemen. India and I (Zulu) do share a large border on a pangea map. Also, we have a MPP and RoP. That is how good the relationship is.
To win the game, I will definitely backstab them.
I know to take out the capital to destroy the space ship, but then they could start another one in their next capital. However, there probably would not be enough time to construct it.